Line bending control for memory applications

ABSTRACT

A method for reducing bending of word lines in a memory cell includes a) providing a substrate including a plurality of word lines arranged adjacent to one another and above a plurality of transistors; b) depositing a layer of film on the plurality of word lines using a deposition process; c) after depositing the layer of film, measuring word line bending; d) comparing the word line bending to a predetermined range; e) based on the word line bending, adjusting at least one of nucleation delay and grain size of the deposition process; and f) repeating b) to e) one or more times using one or more substrates, respectively, until the word line bending is within the predetermined range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/773,689, filed on Nov. 30, 2018. The entire disclosure of theapplication referenced above is incorporated herein by reference.

FIELD

The present disclosure relates to substrate processing systems, and moreparticularly to methods for controlling line bending in memoryapplications.

BACKGROUND

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

Electronic devices such as laptops, tablets, smartphones, etc. includememory such as dynamic random access memory (DRAM) or vertical NAND(VNAND) memory. The memory is typically implemented by an integratedcircuit (IC) including memory cells. As electronic devices shrink insize and use more data, the cost, density and access speed of the memorycells become increasingly important. As a result, feature sizes havedecreased significantly and aspect ratios have increased.

Substrate processing systems for performing deposition and/or etching ona substrate such as a semiconductor wafer typically include a processingchamber with a pedestal. The substrate is arranged on the pedestalduring processing. A process gas mixture including one or moreprecursors may be introduced into the processing chamber to deposit alayer on the substrate or to etch the substrate. In some substrateprocessing systems, radio frequency (RF) plasma can be struck in theprocessing chamber and/or an RF bias on the pedestal may be used toactivate chemical reactions.

SUMMARY

A method for reducing bending of word lines in a memory cell includes a)providing a substrate including a plurality of word lines arrangedadjacent to one another and above a plurality of transistors; b)depositing a layer of film on the plurality of word lines using adeposition process; c) after depositing the layer of film, measuringword line bending; d) comparing the word line bending to a predeterminedrange; e) based on the word line bending, adjusting at least one ofnucleation delay and grain size of the deposition process; and f)repeating b) to e) one or more times using one or more substrates,respectively, until the word line bending is within the predeterminedrange.

In other features, (e) includes adjusting at least one of temperatureand pressure of the deposition process to adjust the nucleation delay.The layer of film is selected from a group consisting of molybdenum,tungsten, ruthenium and cobalt.

In other features, the method includes arranging a liner layer betweenthe plurality of word lines and the layer of film. The liner layerincludes titanium nitride. The temperature of the deposition process isadjusted in e). The pressure of the deposition process is adjusted ine). The temperature and the pressure of the deposition process isadjusted in e). The temperature of the deposition process is decreasedin e) to increase the nucleation delay. The pressure of the depositionprocess is decreased in e) to increase the nucleation delay. Thetemperature and the pressure of the deposition process are decreased ine) to increase the nucleation delay.

In other features, (e) includes increasing the nucleation delay if theword line bending is greater than the predetermined range. In otherfeatures, (e) includes decreasing the nucleation delay if the word linebending is less than the predetermined range.

In other features, (e) includes using an inhibitor species to adjust thenucleation delay. The inhibition species is selected from a groupconsisting of molecular nitrogen and ammonia. A concentration of theinhibitor species is increased in (e) to increase the nucleation delay.An exposure time of the inhibition species is increased in (e) toincrease the nucleation delay. A concentration and an exposure time ofthe inhibitor species are increased in (e) to increase the nucleationdelay.

In other features, (e) includes adjusting precursor chemistry orchanging a mixture of precursors to adjust the nucleation delay. Inother features, (e) includes using at least one of temperature andpressure to control grain size.

In other features, (e) includes using impurities to control grain size.In other features, (e) includes using insitu gases to control grain sizeand film roughness.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIGS. 1 to 5 are side cross-sectional views of an example of a substrateincluding word lines of a memory cell, deposition of a layer over theword lines and bending of the word lines;

FIGS. 6 to 10 are side cross-sectional views of an example of asubstrate including word lines of a memory cell and deposition of alayer over the word lines with significantly reduced bending of the wordlines according to the present disclosure;

FIG. 11 is a flowchart of an example of a method for reducing bending ofword lines when depositing a layer on the word lines;

FIG. 12A is a graph illustrating molybdenum thickness as a function ofALD cycles for different temperatures;

FIG. 12B is a graph illustrating molybdenum resistivity as a function ofthickness at different temperatures;

FIG. 13A is a graph illustrating molybdenum thickness as a function ofALD cycles for different pressures; and

FIG. 13B is a graph illustrating molybdenum resistivity as a function ofthickness at different pressures.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

The substrate processing system can be used to fabricate integratedcircuits such as memory including a plurality of memory cells. As aspectratios increase and critical dimensions shrink, problems may ariseduring fabrication. For example, high aspect ratio features such as wordlines in VNAND and DRAM memory cells may experience bending duringdeposition of film on the word lines. The bending can cause a variety ofproblems such as alignment of the word lines with respect to otherfeatures, performance variations and/or other defects.

The present disclosure relates to a method for reducing bending of highaspect ratio features of a substrate during deposition of film. Forexample, the method may be used to reduce bending of adjacent word linesin memory cells such as VNAND and DRAM. The line bending occurs due tostress during film deposition (metal/dielectric) and cohesive forces ofthe materials.

The method includes modulating the nucleation delay of the depositionprocess to control word line bending. For example, the method includesselecting process parameters for deposition of the film. The processparameters such as temperature and pressure are typically optimized toprovide a smooth film with small grain size and low nucleation delay.However, with small feature sizes and high aspect ratios, line bendingoccurs when smooth film is deposited.

The method according to the present disclosure includes selectingdeposition process parameters, depositing the film and measuring linebending. In some examples, if the line bending is outside of apredetermined range, the temperature and/or pressure are adjusted (e.g.reduced) to increase nucleation delay and grain size to provide arougher film. In some examples, the temperature is adjusted in a rangefrom 300° C. to 700° C. In some examples, the pressure is adjusted in arange from 5 Torr to 80 Torr.

Deposition of the film in this manner reduces line bending at theexpense of fill. The deposition process is run again with newtemperature and pressure values and line bending is measured. Theprocess is repeated until the line bending is within the predeterminedtolerance. In some examples, the method according to the presentdisclosure can significantly reduce line bending of word lines in memorydevices such as VNAND and DRAM memory cells.

Referring now to FIGS. 1 to 5, an example of word line bending duringdeposition of a layer is shown. In FIG. 1, a substrate 100 includes anunderlying layer 114 (including transistors) and a plurality of wordlines 112. In some examples, the plurality of word lines 112 is part ofmemory cells such as a DRAM memory cells, which include a capacitor anda transistor. The plurality of word lines provides a connection to gatesof the transistors. The plurality of word lines 112 controls the flow ofcurrent in a channel of the transistors. In some examples, a liner layer113 is arranged on the plurality of word lines 112 as a barrier layerbefore the metal deposition. For example only, the liner layer 113 maybe made of titanium nitride (TiN), In some examples, the plurality ofword lines 112 may include an outer layer 118 made of dielectric such asSiO₂ and an inner layer made of a material 119 such as silicon (Si) (asshown in dotted lines of adjacent word lines 120 in FIG. 1 but omittedelsewhere for clarity), although other arrangements may be used.

The spacing between the plurality of word lines 112 is predefined. Forexample, the plurality of word lines 112 may be fabricated with uniformspacing d1 between the plurality of word lines 112. In other examples,different spacing can be defined between some of the plurality of wordlines 112. Usually it is desirable to maintain the predefined spacingbetween the plurality of word lines 112 after additional processing isperformed to maintain alignment with other features, to prevent shortingand/or to maintain performance parameters such as resistance and/orcapacitance.

In FIG. 2, a layer 116 is deposited to fill a gap between the pluralityof word lines 112. In some examples, the layer 116 includes tungsten(W), ruthenium (Ru), cobalt (Co), or molybdenum (Mo). In some examples,the liner layer 113 and the layer 116 are deposited using atomic layerdeposition (ALD). In other examples, chemical vapor deposition (CVD) orother deposition process is used. In some examples, plasma may be usedto enhance chemical reactions during deposition. In some examples, thedeposition process parameters for the layer 116 are selected to producethe following characteristics: the layer 116 is conformal and has lownucleation delay and a small grain size. In other words, it is usuallydesirable to have a smooth film deposited on the plurality of word lines112 rather than a rougher film. In some examples, one or more linerlayers may be deposited between the layer 116 and the plurality of wordlines 112.

In FIG. 3, as the layer 116 is deposited with these characteristics,line bending may occur. Some of the plurality of word lines 112 bendtowards an adjacent one of the plurality of word lines 112 and others ofthe plurality of word lines 112 bend away from an adjacent one of theplurality of word lines 112. As a result, the predefined spacing is nolonger maintained. In FIG. 4, additional deposition is performed to fillthe gaps between the plurality of word lines 112.

In FIG. 5, etching and/or other processes may be performed to exposeupper surfaces of the plurality of word lines 112 and/or a top surfaceof the material 119 (to allow contact). Additional layers (not shown)are deposited and contact the material 119. As can be seen, distances d2and d3 between adjacent ones of the plurality of word lines 112 aredifferent than each other and different than d1. When the additionallayers are deposited, misalignment can occur. Additionally, performanceparameters such as resistance and capacitance can be adversely affectedby the variations in spacing between the plurality of word lines 112.

Referring now to FIGS. 6 to 10, an example of a method for reducing wordline bending during deposition of a layer is shown. In FIG. 6, asubstrate 600 includes an underlying layer 114 and a plurality of wordlines 112. The spacing between the plurality of word lines 112 ispredefined. For example, the plurality of word lines 112 is fabricatedwith uniform spacing d1 between the plurality of word lines 112. Inother examples, different spacing can be defined between some of theplurality of word lines 112. Usually it is desirable to maintain thepredefined spacing between the plurality of word lines 112 afteradditional processing is performed to maintain alignment with otherfeatures, to prevent shorting and/or to maintain performance parameterssuch as resistance and/or capacitance.

In FIG. 7, a layer 616 is deposited to fill a gap between the pluralityof word lines 112. In some examples, the layer 616 is deposited usingatomic layer deposition (ALD), chemical vapor deposition (CVD) or otherdeposition process. In some examples, plasma may be used to enhancechemical reactions during deposition. In some examples, the depositionprocess parameters for the layer 616 are selected to produce thefollowing characteristics: the layer 616 is conformal and has highnucleation delay and a large grain size. As will be described furtherbelow, depositing film using high nucleation delay and the large grainsize will result in rougher film characteristics but will prevent linebending. In other words, the method described herein goes against theusual goal of depositing a smooth film on the plurality of word lines112.

In FIG. 8, as the layer 616 is deposited with these characteristics,line bending is reduced significantly. In FIG. 9, additional depositionis performed to fill the gaps between the plurality of word lines 112.

In FIG. 10, etching and/or another process may be performed to exposeupper surfaces of the plurality of word lines 112. As can be seen inFIG. 10, additional layers (not shown) can be deposited on an uppersurface 1010 and may require alignment with top surfaces of the material119. As can be seen, the predefined distance (e.g. d1 in this example)between adjacent ones of the plurality of word lines 112 is maintained.Therefore, substantial alignment can be maintained when the additionallayers are deposited. Additionally, performance parameters such asresistance and capacitance are not adversely affected by the variationsin spacing between the plurality of word lines 112 (as in FIGS. 1 to 5).

Referring now to FIG. 11, a method 1100 for reducing bending of afeature such as word lines when depositing a layer on the feature isshown. The method 1100 includes selecting process parameters fordeposition of the film at 1110. The process parameters such astemperature and pressure are typically optimized to provide a smoothfilm with small grain size and low nucleation delay. However, with smallfeature sizes and high aspect ratios, line bending occurs when smoothfilm is deposited.

After selecting process parameters, the method includes depositing thefilm at 1114. At 1118, line bending is measured and compared to apredetermined range. If the line bending is outside of the predeterminedrange as determined at 1118, the nucleation delay and/or grain size areadjusted. In some examples, the temperature or pressure used duringdeposition are varied as described herein although other methods aredescribed below.

For example when the line bending is higher than the predeterminedrange, the pressure and/or temperature are decreased. The process is runagain at 1126 with the adjustment. The method returns to 1118 and linebending is measured again. The process may be repeated one or more timesuntil the line bending is within the predetermined range as determinedat 1118. In other words, balancing of film roughness and line bendingmay be optimized. When 1118 is true, the process is used for producingsubstrates.

Referring now to FIGS. 12A and 12B, lowering the temperature duringdeposition increases nucleation delay, grain size and roughness of thefilm. As a result, the word line bending is reduced. In FIG. 12A, agraph illustrates molybdenum thickness as a function of ALD cycles fordifferent temperatures. In this example, the higher temperaturecorresponds to 590° C. and the lower temperature corresponds to 550° C.As can be seen, the nucleation delay for the lower temperature isincreased relative to the higher temperature (in this example from about33 ALD cycles to about 62 ALD cycles). The grain size and roughness ofthe film also increases. In some examples, the word line bendingdecreases from 9.6 nm to 1.7 nm. In FIG. 12B, a graph illustratesmolybdenum resistivity as a function of thickness at differenttemperatures. The different temperatures have approximately the sameresistance.

Referring now to FIGS. 13A and 13B, lowering the pressure duringdeposition increases nucleation delay, grain size and roughness of thefilm. As a result, the word line bending is reduced. In FIG. 13A, agraph illustrates molybdenum thickness as a function of ALD cycles fordifferent pressures. In this example, the higher pressure corresponds to60 Torr and the lower pressure corresponds to 40 Torr. As can be seen,the nucleation delay for the lower pressure is increased relative to thehigher pressure (in this example from about 39 ALD cycles to about 59ALD cycles). The grain size and roughness of the film also increases. Insome examples, the word line bending decreases from 9.9 nm to 1.6 nm. InFIG. 13B, a graph illustrates molybdenum resistivity as a function ofthickness at different pressures. The different pressures haveapproximately the same resistance.

As can be appreciated, a combination of temperature and pressure changescan be used to increase nucleation delay, grain size and roughness andreduce line bending.

While examples set forth above describe modulating the nucleation delayby varying temperature and/or pressure, there are other ways to modulatenucleation delay. For example, the nucleation delay can be modulated byselecting a different deposition process (atomic layer deposition (ALD),chemical vapor deposition (CVD) or plasma enhanced (PE) ALD), selectinga different conductor (molybdenum (Mo), tungsten (W), ruthenium (Ru), orcobalt (Co) or different precursors for the conducting layer,introducing impurities before deposition or during deposition to altergrain size or nucleation delay, or using a surface treatment such asmolecular nitrogen (N₂ or ammonia (NH₃)) prior to deposition. Thesurface treatment may include the use of plasma.

When using an ALD process, precursor molecules need to chemically adsorbto the surface before film growth can be initiated. The surfacecomprises finite nucleation sites to which the precursor molecules canadsorb. When these sites are competitively blocked with molecules thatcan also adsorb to the surface but minimally interact with the precursormolecules, the sites are no longer available for precursor adsorption.

By varying the concentration of the inhibitor molecules, nucleationdelay and consequently film roughness and line bending can becontrolled. Small nitrogen containing molecules such as molecularnitrogen (N₂) or ammonia (NH₃) may be effective inhibitors. In otherexamples, larger nitrogen containing molecules such as hydrazine ororganic hydrazines can be used. The larger molecules are more potent asan inhibitor due to the additional effect of steric hindrance.

Some examples described above start with a smooth film and decrease thetemperature and/or pressure until the desired line bending threshold isreached. In other examples, the method can be performed initially with arougher film and the temperature and/or pressure can be increased untilthe desired amount of line bending is reached. In other words, a desiredtradeoff between line bending and roughness can be determined fromeither direction smooth to rough or rough to less rough. For example, apredetermined threshold range can be used. The word line bending iscompared to the predetermined threshold range. If the word line bendingis less than the predetermined threshold range, then nucleation delay isdecreased until the word line bending is in the predetermined thresholdrange. If the word line bending is greater than the predeterminedthreshold range, then nucleation delay is increased until the word linebending is in the predetermined threshold range.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.Further, although each of the embodiments is described above as havingcertain features, any one or more of those features described withrespect to any embodiment of the disclosure can be implemented in and/orcombined with features of any of the other embodiments, even if thatcombination is not explicitly described. In other words, the describedembodiments are not mutually exclusive, and permutations of one or moreembodiments with one another remain within the scope of this disclosure.

Spatial and functional relationships between elements (for example,between modules, circuit elements, semiconductor layers, etc.) aredescribed using various terms, including “connected,” “engaged,”“coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and“disposed.” Unless explicitly described as being “direct,” when arelationship between first and second elements is described in the abovedisclosure, that relationship can be a direct relationship where noother intervening elements are present between the first and secondelements, but can also be an indirect relationship where one or moreintervening elements are present (either spatially or functionally)between the first and second elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A OR BOR C), using a non-exclusive logical OR, and should not be construed tomean “at least one of A, at least one of B, and at least one of C.”

What is claimed is:
 1. A method for reducing bending of word lines in amemory cell, comprising: a) providing a substrate including a pluralityof word lines arranged adjacent to one another and above a plurality oftransistors; b) depositing a layer of film on the plurality of wordlines using a deposition process; c) after depositing the layer of film,measuring word line bending; d) comparing the word line bending to apredetermined range; e) based on the word line bending, adjusting atleast one of nucleation delay and grain size of the deposition process;and f) repeating b) to e) one or more times using one or moresubstrates, respectively, until the word line bending is within thepredetermined range.
 2. The method of claim 1, wherein (e) includesadjusting at least one of temperature and pressure of the depositionprocess to adjust the nucleation delay.
 3. The method of claim 1,wherein the layer of film is selected from a group consisting ofmolybdenum, tungsten, ruthenium and cobalt.
 4. The method of claim 1,further comprising arranging a liner layer between the plurality of wordlines and the layer of film.
 5. The method of claim 4, wherein the linerlayer includes titanium nitride.
 6. The method of claim 2, wherein thetemperature of the deposition process is adjusted in e).
 7. The methodof claim 2, wherein the pressure of the deposition process is adjustedin e).
 8. The method of claim 2, wherein the temperature and thepressure of the deposition process are adjusted in e).
 9. The method ofclaim 2, wherein the temperature of the deposition process is decreasedin e) to increase the nucleation delay.
 10. The method of claim 2,wherein the pressure of the deposition process is decreased in e) toincrease the nucleation delay.
 11. The method of claim 2, wherein thetemperature and the pressure of the deposition process are decreased ine) to increase the nucleation delay.
 12. The method of claim 1, wherein(e) includes increasing the nucleation delay if the word line bending isgreater than the predetermined range.
 13. The method of claim 1, wherein(e) includes decreasing the nucleation delay if the word line bending isless than the predetermined range.
 14. The method of claim 1, wherein(e) includes using an inhibitor species to adjust the nucleation delay.15. The method of claim 14, wherein the inhibition species is selectedfrom a group consisting of molecular nitrogen and ammonia.
 16. Themethod of claim 14, wherein a concentration of the inhibitor species isincreased in (e) to increase the nucleation delay.
 17. The method ofclaim 14, wherein an exposure time of the inhibition species isincreased in (e) to increase the nucleation delay.
 18. The method ofclaim 14, wherein a concentration and an exposure time of the inhibitorspecies are increased in (e) to increase the nucleation delay.
 19. Themethod of claim 1, wherein (e) includes adjusting precursor chemistry orchanging a mixture of precursors to adjust the nucleation delay.
 20. Themethod of claim 1, wherein (e) includes using at least one oftemperature and pressure to control grain size.
 21. The method of claim1, wherein (e) includes using impurities to control grain size.
 22. Themethod of claim 1, wherein (e) includes using insitu gases to controlgrain size and film roughness.